Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Processes S2 > Thermoforming and Casting > Flashcards

Thermoforming and Casting Flashcards

1
Q

Thermoforming Process: Heating

A

Usually by radiant electric heaters, located on one or both sides of starting plastic sheet at roughly 125mm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Thermoforming Overview

A
  • Relies on softening thermoplastic above Tg for amorphous polymers or slightly below Tm for semicrystalline
  • Common plastics: PS, cellulose acetate and CAB, ABS, PVS, PMMA, PE and PP
  • Examples: food packaging (mostly film), advertising signs. refridgerator liners, manufacturing collation trays etc.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Thermoforming Process

A
  1. Clamp a sheet of material
  2. Heat to the sag point
  3. Force against the surface of a mould by the use of a vauum, or air pressure, or both
  4. Cool and remove
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Methods of Thermoforming

A
  • Vacuum forming
  • Pressure forming
  • Mechanical forming
  • Free blowing
  • Drape forming
  • Plug-assisted forming
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Vacuum Forming Process

A
  1. Sheet clamped in frame and heated
  2. When sheet is rubbery, heat is removed and it’s placed in a concave mould cavity
  3. Vacuum draws the sheet into the cavity
  4. Plastic hardens on contact with cold mould surface - removed then trimmed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Pressure Forming Process

A
  1. Sheet is placed over a mould cavity
  2. Positive pressure forces the sheet into the cavity
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Mechanical Forming Process

A
  1. Clamp heated rubbery sheet between two mould halves
  2. Once mould is closed, vacuum is applied to the female half of the mould
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Positive and Negative Moulds

A
  • A positive (or male) mould has a convex shape
  • A negative (or female) has a concave cavity
  • Each produces a different pattern of thinning in a given part
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Free Blowing

A
  • Part-spherical shapes can be produced by simple blow forming of heated sheets of thermoplastics
  • Can also be blown into shaped female moulds
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Thermoforming Advantages

(4)

A
  • Inexpensive tooling (often Al)
  • Vacuum mould requires holes placed in appropriate positions - size less than 0.5mm to avoid leaving marks
  • Medium production rates
  • Scrap is 15-50% (called skeletal) - recycled to sheet extruders or for secondary use
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Thermoforming Disadvantages

(3)

A
  • High part cost relative to injection moulded parts
  • Non-uniform gauge due to film stretching
  • Process is limited by geometry
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Casting Thermoplastics

A
  • Monomer, catalyst, activators are mixed and heated above m. pt (part formed after polymerisation)
  • Materials include: acrylics, polystyrene, polyamides (nylons) and vinyl (PVC)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Casting Thermosets

A
  • Mixed and poured
  • Materials include: epoxies, phenolics, ployurethanes, polyesters
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Casting Products

A

Gears (nylon), bearings, wheels, thick sheets, lenses, components requiring resistance to war

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Casting Processes

A
  1. Monomers casting
  2. Potting and encapsulation
    - Mould is simpler (less costly)
    - Cast item is free of residual stress and viscoelastic memory
    - Suited to low production quantities
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Monomer Casting

A
  • Uses controlled chemical reaction of polymer materials
  • Monomer is mixed with a catalyst, additives etc, before pouring - mixture then polymerises
  • Moulds can be epoxy, plaster, wood, sheet metal or even rubber
  • Produces high molecular mass polymer sheet for certain thermoforming applications (e.g. aircraft windows)
17
Q

Monomer Cating Advantage

A

Requires minimum capital expenditure

18
Q

Monomer Casting Disadvantage

A

Difficult to automate

19
Q

Potting and Encapsulation

A
  • Processes for electrical assemblies where the surrounding serves as a dielectric
  • Involves casting liquid resin (e.g. epoxies, urethanes and silicones) around an electrical component (e.g. transformer) to embed it in the plastic
  • Used in applications where components need protection (e.g. physical and thermal shock, vibration, moisture, corrosion)
20
Q

Applications of Potting and Encapsulation

A

Electronic and electrical components, sensor assemblies, power supplies, PCBs, transformers

21
Q

Potting

A

Comonent is covered in resin to guard it against potential environmental threats or to insulate electrically using a “pot” housing or case, which becomes part of the component

22
Q

Encapsulation

A
  • Involves placing the assembly or component within a machined cavity of a mould tool
  • Then tool is then filled with casting resin until set
  • Component and hardened resin are then removed from the mould to be placed in an assemble
23
Q

Advantages of Potting and Encapsulation

(7)

A
  • Non-corrosive
  • Resistes moisture, vibration and T extremes
  • Enhances electrical insulation
  • Flame retardent resins available
  • Improves assembly robustness
  • Design in strain relief
  • Custom designs/shapes and logos possible
24
Q

Disadvantage of Potting and Encapsulation

A

Heat from the curing reaction may cause damage to components

Processes S2 (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions